1. Field of the Invention
The present invention relates to a method for assessing the risk of developing prostate cancer in an individual. Increased risk for prostate cancer is correlated with high insulin-like growth factor status (IGF status). Specifically, the method involves measurement of IGF-I and/or insulin-like growth factor binding protein-3 (IGFBP-3) in a specimen. High levels of IGF and/or low levels of IGFBP correlate with increased risk of developing prostate cancer.
In an alternative embodiment, the method involves determining the IGF/PSA status of an individual wherein the determination of IGF status is combined with a measurement of prostate specific antigen (PSA) levels. The IGF/PSA status provides an improved method of assessing the prognosis of existing prostate cancer.
Furthermore, novel treatment modalities are suggested by the discovery of the link between IGF-axis component levels and prostate cancer that involve modulating IGF-axis component levels.
2. Description of the Prior Art
Prostate adenocarcinoma accounts for the majority of malignancies in males over the age of 65. Yearly screening for prostate cancer is recommended after the age of 45. There has been considerable effort toward identifying suitable prostate cancer markers to assist in predicting, diagnosing and monitoring this disease.
Prostate specific antigen (PSA) is recognized as the most sensitive marker of prostatic adenocarcinoma (M. K. Brawer Cancer 71(suppl):899-905 (1993); J. E. Oesterling J. Urol. 145:907-23 (1991)). PSA is also recognized as a proven screening vehicle (P. H. Gann, et al. Amer. Med. Assoc. 273:289-94 (1995); W. J. Catalona, et al. J. Urol. 151:1283-90 (1994)). It has been the most sensitive front line test for identifying prostate gland-contained, and hence presumably curable, cancer. PSA has also been useful in detecting clinically significant tumors, as opposed to latent, indolent micro-carcinomas. Screening for PSA is even superior to the common office practice of digital rectal examination (DRE). For example, Labrie et al. (Clin. Invest. Med. 16:425-39 (1993)) showed that 97% of cancers detected at annual follow-up by DRE plus PSA testing were PSA-positive. Thus, only a minimal benefit accrues from including DRE in the medical evaluation.
Investigators have searched for other markers or indicators of prostate cancer, but to date PSA has been the most useful marker. No one has heretofor studied the association of IGF-axis components with prostate cancer.
Insulin-like growth factors (IGF-I and IGF-II) belong to family of peptides that mediate a broad spectrum of growth hormone-dependent as well as independent mitogenic and metabolic actions. Unlike most peptide hormones, IGFs in circulation and other physiological fluids are associated with a group of high affinity binding proteins (IGFBPs) that specifically bind and modulate their bioactivity at the cellular level. Under normal conditions about 95-98% or the IGF-I in human plasma is bound to IGFBPs. Six structurally homologous IGFBPs with distinct molecular size, hormonal control, and tissue expression and functions, have been identified (J. I. Jones, et al. Endocrinol. Reviews 16:3-34, (1995)). Most serum IGF-I circulates in a relatively stable ternary complex consisting of IGFBP-3 and a unique leucine-rich, acid-labile subunit (ALS). Less than one percent of IGF-I is estimated to exist in a xe2x80x9cfreexe2x80x9d or unbound form.
The rate of cell proliferation is positively correlated with risk of transformation of certain epithelial cell types. S. M. Cohen and L. B. Ellwein. Science 249:1007 (1990); S. M. Cohen and L. B. Ellwein. Cancer Research 51:6493 (1991). IGFs have mitogenic and anti-apoptotic influences on normal and transformed prostate epithelial cells. A. Y. Hsing, K. Kadomatsu, M. J. Bonharn, D. Danielpour. Cancer Research 56:5146 (1996); Z. Culig, A. Hobisch, M. V. Cronauer, C. Radmayr, J. Trapman, A. Hittmair, G. Hartsch, B. Klocker. Cancer Research 54:5474 (1994); P. Cohen, D. M. Peehl, R. G. Rosenfeld. Hormone and Metabolic Research 26:81 (1994); M. Iwamura, P. M. Stuss, J. B. Casamento, A. T. Cockett. Prostate 22:243 (1993); P. Cohen, D. M. Peehl, G. Lamson, R. G. Rosenfeld. J. Clinical Endocrinology and Metabolism 73:401 (1991); R. Rajah, D. Valentino, and P. Cohen. J. Biol. Chem. 272:12181 (1997). Most circulating IGF-I originates in the liver, but IGF bioactivity in tissues is related not only to levels of circulating IGFs and IGFBPs, but also to local production of IGFs, IGFBPs, and IGFBP proteases. J. J. Jones and D. R. Clemmons. Endocrine Reviews 16:3 (1995). Person-to-person variability in levels of circulating IGF-I and IGFBP-3 (the major circulating IGFBP (J. J. Jones and D. R. Clemnmons. Endocrine Reviews 16:3 (1995) is considerable (A. Juul, P. Bang, N. T. Hertel, K. Main, P. Dalgaard, K. Jorgensen, J. Muller, K. Hall, N. E. Skakkebaek. J. Clinical Endocrinology and Metabolism 78:744 (1994); A. Juul, P. Dalgaard, W. F. Blum, P. Bang, K. Hall, K. F. Michaelsen, J. Muller, N. E. Skakkeback. J. Clinical Endocrinology and Metabolism 80:2534 (1995) and heterogeneity in serum IGF-I level appears to reflect heterogeneity in tissue IGF bioactivity. Acromegaly and growth hormone deficiency are examples where there are clear changes in tissues that are correlated with serum IGF-I level, implying a relationship between serum IGF-I level and tissue IGF-I bioactivity. Also, factors that decrease circulating IGF-I level also affect expression of genes in target organs for IGF-I action in a manner that decreases IGF bioactivity. For example, antiestrogens lower IGF-I level (M. Pollak, J. Constantino, C. Polyochronakos, S. Blauer, H. Guyda, C. Redrnond, B. Fisher, R. Margolese. JNCI 82:1693 (1990), but also increase IGFBP expression (H. Huynh, X. Yang, B. Deroo, M. Pollak. Cell Growth and Differentiation 7:1501 (1996); H. Huynh, X. Yang, M. Pollak. J Biol Chem 271:1016 (1996) and decrease IGF-I receptor expression (H. Huynh, T. Nickerson, M. Pollak. Clinical Cancer Research 2:2037 (1996) in cells that are targets for IGF-I action. No one has heretofore shown that markers relating to IGF-axis components can also be used as a risk marker for prostate cancer.
Abbreviations and Definitions
AAGxe2x80x943xe2x80x94alpha-androstanediol glucuronide.
ALSxe2x80x94Acid Labile Subunit. A protein found in the 150 KDa ternary complex wherein most of the circulating IGF is found. ALS is sensitive to inactivation by acid.
Binary complexxe2x80x94A two part complex of IGFBP and ALS or IGFBP and IGF.
Body fluidxe2x80x94Any biological fluid, including but not limited to the following: serum, plasma, lymph fluid, synovial fluid, follicular fluid, seminal fluid, amniotic fluid, milk, mammary fluid, whole blood, urine, spinal fluid, saliva, sputum, tears, perspiration, mucus tissue culture medium, tissue extracts and cellular extracts. Preferably, the body fluid is blood, plasma, serum or seminal fluid.
DHTxe2x80x94Dihydrotestosterone.
GHxe2x80x94Growth hormone.
GHBPxe2x80x94GH binding protein.
IGFxe2x80x94Insulin-like Growth Factor.
IGFxe2x80x94axis componentsxe2x80x94Those components that modulate the IGF/GH cascades including GH, GHBP, GH receptor, IGF, IGF receptor, IGF proteases, IGFBP 1 through 6 and other IGFBPs, ALS, IGF proteases, IGF and GH receptor antagonists, and the like.
IGFxe2x80x94axis component modulating agentxe2x80x94also: IGF status modulating agents. Includes any agent whose intended effect is to influence the GH or IGF cascades. Agents include GH, GHBP, IGF, IGFBP, ALS, IGFBP complex, GH receptors, IGF receptors, antibodies or modulators of any of the preceding, receptor antagonists for GH or IGF, or any drug that acts to modulate the IGF status of an individual including somatostatin, somatostatin analogues, GH antagonists, IGF antagonist, IGFBP stimulator, and the like.
IGFBPxe2x80x94Any IGF binding protein, including IGFBP-1 to 6 and the heretofore unsequenced IGFBPs. Preferably, the IGFBP is IGFBP-3 in the context of the assay described herein.
IGFBP-3xe2x80x94The major circulating IGF binding protein.
IGFBP complexxe2x80x94This term is defined herein to include either the binary complex of IGFBP and ALS or IGF or the ternary complex of IGFBP and ALS and IGF.
IGF statusxe2x80x94The IGF status of an individual is reflected in the levels of IGF-axis components. For example a high IGF status is reflected by high levels of IGF and stimulators of IGF activity and low levels of inhibitors of IGF activity such as IGFBP. The IGF status of an individual is now known to vary -either up or down-in in certain conditions involving the prostate, including but not limited to, prostate adenocarcinoma or benign prostatic hyperplasia.
IGF/PSA statusxe2x80x94A combination of IGF status and PSA levels. Individuals with high IGF/PSA status are at risk for developing severe prostate cancer. A high IGF/PSA status is reflected by high IGF and PSA levels and low IGFBP levels.
RRxe2x80x94Relative risk.
Risk Indexxe2x80x94A value indicating the risk of a patient for developing prostate disease or poor prognosis for patients with prostate disease. The risk index can be generated from data concerning the IGF-axis component levels in a patient, including IGF or IGFBP levels and/or the PSA levels of a patient.
SHBGxe2x80x94Sex hormone binding globulin.
Txe2x80x94Testosterone.
Ternary complexxe2x80x94The 150 KDa complex composed of IGF, IGFBP and ALS.
Treatment designed to influence IGF statusxe2x80x94Includes any medical treatment whose intended effect is to influence the GH or IGF cascades. Treatments may include treatments with such agents as GH, GHBP, IGF, IGFBP, ALS, IGFBP complex, GH receptors, IGF receptors, antibodies or inhibitors of any of the preceding, receptor antagonists for GH or IGF, or any drug that acts to modulate the IGF-axis status of an individual. Individuals include both human and animals, such as pigs, cattle, sheep, goats, horses, poultry, cats, dogs, fish, etc.
The present invention relates to assays for measuring IGF-I levels and their use for predicting, diagnosing and monitoring prostate cancer. A strong consistent positive association between IGF-I and prostate cancer risk has been observed, especially with adjustment for IGFBP-3. High levels of IGF-I are predictive of increased risk for prostate cancers, whereas IGFBP has a protective effect. Additionally, the IGF or IGF/IGFBP assay can be combined with a test for PSA for improved ability to predict patient prognosis and monitor treatment. Further, these findings suggest that it is possible to treat prostate cancers with agents that modulate the IGF-axis components.
In the its broadest embodiment, a method of predicting increased risk of prostate cancer in an individual is provided. The method involves measuring the xe2x80x9cIGF statusxe2x80x9d or concentration of IGF-axis components in a body fluid from an individual, wherein changes in the IGF status or concentration of IGF-axis components as compared to normal reference values indicates an increased risk for prostate cancer.
In one embodiment, the invention is a method of predicting increased risk of prostate cancer in an individual, comprising measuring the concentration of insulin-like growth factor (IGF-I) in a body fluid from an individual, wherein an elevated concentration of IGF-I above a reference range for IGF-I indicates an increased risk for prostate cancer.
In another embodiment, the invention is a method of predicting increased risk of prostate cancer in an individual. The method involves measuring the concentration of IGF-I and IGFBP in a specimen from an individual, wherein increased IGF-I and decreased IGFBP, as compared to a normal reference range value, indicates an increased risk for prostate cancer.
In yet another embodiment, the invention is a method of measuring the IGF/PSA status of an individual. High IGF and PSA levels and/or low IGFBP levels are indicative of individuals at risk for severe prostate cancer or who have prostate cancer with a poor prognosis.
A multivariate adjustment of the IGF-I concentration relative to the IGFBP-3 concentration provides an adjusted IGF-I level or xe2x80x9cIGF statusxe2x80x9d which can be compared to an adjusted normal reference range value. An algorithm can be designed, by those with skill in the art of statistical analyses, which will allow the user to quickly calculate an adjusted IGF level or xe2x80x9cIGF statusxe2x80x9d for use in making predictions or monitoring prostate disease. With additional patient data, generated similarly to the manner described herein, it will be possible to more accurately define normal reference range values for IGF status parameters. The algorithm and normal reference values can be used to generate a device that will allow the end user to input IGF, IGFBP and quickly and easily determine the IGF status or risk index of an individual. Similarly, it is possible to provide a device that indicates the IGF/PSA status of an individual.
Finally, the invention pertains to a method of treating prostate cancer, comprising administering an IGF-axis component modulating agent to an individual with prostate cancer.
As used herein the term xe2x80x9cprostate diseasexe2x80x9d includes diseases or disorders associated with pathologic conditions of the prostate, including, but not limited to prostate cancer or benign prostatic hyperplasia. The method of the present invention is most preferably used to determine the risk of an individual developing prostate cancer, diagnosing prostate cancer or assessing the progress of the cancer. Accordingly, the method of the present invention may be useful in predicting prostate cancer, differentiating cancer from other prostatic diseases.
A suitable specimen is collected from an individual. Suitable specimens include any body fluid or tissue known to contain IGF-axis components and/or PSA. Preferably, the specimen is blood, serum, plasma or seminal fluid. The specimen may be collected by venipuncture or capillary puncture, and the specimen collected into an appropriate container for receiving the specimen. Alternatively, the specimen may be placed onto filter paper.
The IGF-axis components and/or PSA can be measured by techniques well known to those skilled in the art, including, but not limited to immunoassays such as enzyme-linked immunosorbent assay (ELISA), enzyme immunoasssay (EIA), fluorescence polarization immunoassay (FPIA), fluorescence immunoassay (FIA) and radioimmunoassay (RIA). The assays described in U.S. application Ser. Nos. 08/626,641, 08/643,830, 08/763,244 and 08/829,094 are particularly suitable and are incorporated herein by reference. Further, the concentrations of the IGF-axis components and/or PSA may, for example, be measured by test kits supplied by DIAGNOSTIC SYSTEMS LABORATORIES, INC., Webster, Tex., USA.
In a preferred embodiment, total IGF-I can be measured. In some cases, it may be advantageous to measure total, bound and/or free IGF-I. For example, suitable highly specific and simple non-competitive ELISAs for reliable determination of IGF-I (M. J. Khosravi, et al., 1996 Clin. Chem. 42:1147-54), IGFBP-3 (Khosravi J. et al. 1996 Clin. Chem. S6:234) and IGFBP-1 (M. J. Khosravi, et al. 1996 Clin. Chem. S6:171) have been described. The high affinity antibodies incorporated in these immunoassays have been selected for lack of cross-reactivity or interference by the closely related peptides or binding protein.
Additionally, IGFBPs can be used as an indicator of decreased risk for prostate cancer. Preferably, the binding protein is IGFBP-3 and total, complexed and/or free IGFBP-3 may be measured. In alternative embodiments, the other IGFBPs (such as, but not limited to IGFBP-1) may also be used to predict the risk of prostate cancer. Additionally, acid-labile subunit (ALS) may also be used to predict susceptibility to prostate cancer. The ALS may be total ALS, complexed and/or free ALS. Other IGF-axis components may also influence the risk of prostate cancer.
Men in the highest quartile of circulating IGF-I have a relative risk of prostate cancer of 4.32 (95 percent confidence interval (CI) 1.76-10.6) compared to men in the lowest quartile, and there was significant linear trend such that a 100 ng/ml increase in IGF-I level was associated with a doubling of risk (p=0.001). Furthermore, this association is evident among men with normal as well as elevated baseline prostate specific antigen (PSA) levels. These results indicate that circulating IGF-I is predictor of prostate cancer risk, and perhaps progression, and thus have implications for risk reduction and treatment strategies.